This invention relates to methods of bonding a fabric layer to a cellular foam layer to form a laminate that is then applied with adhesive to a pad of the type used for cushions, in particular for seating and back cushions in automotive seats.
Fabric covered foam articles, such as cushions, generally comprise a foam pad adhesively secured to a covering fabric. Lear Seating Corporation of Southfield, Mich. developed a particular bonding method that is described in U.S. Pat. No. 4,692,199, issued Sep. 8, 1987 to Kozlowski. In that method, vacuum pressure is applied to a porous contoured mold in order to draw an impervious adhesive film against a cloth fabric layer to conform the cloth fabric layer and adhesive to the contours of the inner mold surface. A matching cellular foam pad is placed in mating engagement with the adhesive film as it is held to the contour of the mold surface by vacuum pressure. The foam pad may then be compressed against the mold by a perforated platen and held in place. The vacuum may be discontinued. A heated fluid, preferably steam is supplied through the porous mold to heat and diffuse the adhesive film into the adjacent fabric layer and cellular foam pad, respectively, to adhesively secure the two together. Vacuum may then be applied to remove moisture from the fabric and foam by drawing air through the perforations in the platen and through the foam pad, fabric layer and porous mold.
Variations to this method of bonding fabric layers to cushions are disclosed in U.S. Pat. No. 5,232,543, issued Aug. 3, 1993 to Frelich, et al., and U.S. Pat. No. 5,338,386, issued Aug. 16, 1994 to Frelich, et al. These patents show a method and apparatus for bonding fabric to seat cushion trenches in which portions of a fabric bag may be bonded to the seat cushion, then manipulated to remove wrinkles before the rest of the fabric bag is bonded to the cushion.
In addition, U.S. Pat. No. 5,254,197, issued Oct. 19, 1993 to Klems, discloses another variation on the method and apparatus for adhesively bonding a fabric layer to cellular foam pad in which a heat sensitive adhesive is activated by microwave radiation.
For all applications in which a fabric is adhesively bonded to a cellular foam pad, and particularly for automotive seat cushions, the adhesive must securely bond the foam and fabric together. Incomplete bonding permits the foam cushion to settle and bunch and shift position relative to the fabric. This condition causes excessive wear on the fabric and on the cushion, and causes the fabric to crease or wrinkle. Creases and wrinkles not only have an unsightly appearance, but also present areas more susceptible to wear and tear.
Following development of the bonding method disclosed in Kozlowski (U.S. Pat. No. 4,692,199), it was found that bonding between the fabric and the cushion could be improved if a thin layer of cellular foam material was first flame laminated to the underside of the fabric. Then, following the known bonding method of Kozlowskl, the foam-fabric laminate was attached to the cushion, such that the adhesive penetrated into the cellular foam of the foam-fabric laminate and into the core cushion.
Bond strength is a measure of the force per square inch required to separate the laminated fabric from the cellular foam pad. None of the prior patents set out above specify the bond strengths obtained. None of the prior patents specify the types of foam that are best suited for use as the cellular foam pad or as the foam layer used to form a laminate with the fabric prior to attachment to the cellular foam pad or cushion. Applicant has surprisingly found that consistently excellent bond strengths not heretofore achieved are obtained when a foam-fabric laminate is used in the bonding methods disclosed in these prior patents, wherein the foam layer of the foam-fabric laminate comprises certain polyurethane foams formed with a polymeric methylene diphenyl diisocyanate/toluene diisocyanate (MDI/TDI) blended isocyanate or a polymeric methylene diphenyl diisocyanate.